Police and rescue workers have warned against jumping from Tower Bridge into the River Thames after a man understood to be making a film had to be rescued from the water by two bystanders. Toby Green and George Pearse, both 23, jumped into the river to rescue a man, understood to be Josh Burton, a film-maker from south-east London, who police say jumped from the bridge as part of a stunt on Sunday. The men were playing chess by the Thames – a weekly ritual of theirs – when they heard the splash. “We looked around and there was a body flailing around in the water, just below Tower Bridge. It was clear that someone had just jumped or fallen off the bridge. The person’s head was sort of underwater a bit and he looked like he couldn’t swim, being hit by the shock of water,” Green said. “So we immediately chucked off our clothes and jumped in. It looked like he was drowning.” The RNLI appealed for people not to pull such pranks, warning of the serious dangers of jumping into the river. “We do occasionally respond to emergency calls where people have used the Thames to film stunts for social media channels and we would strongly urge against this. The river may appear benign, but it is an incredibly dangerous environment and is not the place to try any kind of stunt,” a spokesman said on Monday. “Jumping from a height into the river brings all kinds of hazards. The Thames is a very fast-flowing river, running twice as fast as an Olympic swimmer can swim, so anyone jumping in will be swiftly swept away. “There is also the danger of hitting hidden obstacles, particularly close to shore. A tidal range of seven metres means there’s a huge difference in the depth of the water between high and low tide.” Even if a jumper didn’t hit an obstacle, the spokesman added, jumping from height can leave people severely winded and there is a danger of suffering cold-water shock which can result in drowning. Pearse, an experienced open-water swimmer, was the first to jump in and make it to the man. Pearse held his head above the water while Green went to grab a lifebuoy, before jumping in the water himself to help. “We were just thinking: ‘Keep our heads above the water and go help this guy … get to him before he drowns,’” he said on Monday. He said a crowd of people gathered to help haul the man towards the embankment and the three of them managed to make it to a ladder to climb out. It was only at that point, Green said, that they realised the man was wearing a wetsuit underneath his suit and had evidently jumped into the river intentionally. “It was obviously very, very disrespectful of him,” Green said, stressing that the emergency services had had to be called. “It’s not on but I’m glad he’s safe.” City of London police said they were called out on Sunday at about 11.55am to “reports that a man, 27, had jumped into the River Thames from Tower Bridge”. The force said: “The man jumped into the river as part of an online video. He managed to safely get out of the river and didn’t suffer any injuries. The force has opened an investigation and are currently looking into the incident.” It warned that jumping into the River Thames from a bridge “for your own entertainment or to entertain others” is extremely dangerous and is a serious risk to the life of anyone who attempts it. The force said doing so obliged the emergency services to respond, taking them away from more critical incidents. “If you do purposefully jump into the Thames for reasons of this nature, you may also face enforcement action from the police, so be warned.” Speaking to the Guardian on Monday, Burton said only that he was “calm” when he jumped and that he had worn the wetsuit to be “safe [rather] than sorry”, citing an open police investigation.